Conventionally, power transmission systems include contact type systems that transmit power using wires such as power codes and electric power cables and contactless type systems without such wires. As an example of the contactless type power transmission systems, a system using magnetic field resonance is known. For example, a contactless type power transmission system described in Patent Document 1 includes a power-sending device including a primary-side resonance coil and a power-receiving device having a secondary-side resonance coil. The primary-side resonance coil receives alternating current power from an alternating current power supply. Magnetic field resonance occurs between the primary-side resonance coil and the secondary-side resonance coil. Through such magnetic field resonance between the primary-side resonance coil and the secondary-side resonance coil, the alternating current power is transmitted from the power-sending device to the power-receiving device.